Hash.index deprecated

ruby 1.9

irb(main):001:0> {1=>2}.index(2)
(irb):18: warning: Hash#index is deprecated; use Hash#key
=> 1
irb(main):002:0> {1=>2}.key(2)
=> 1

ruby 1.8.6

irb(main):001:0> {1=>2}.index(2)
=> 1

Action: use Hash.key